1. Field of the Invention
This invention relates to an improved loom harness, and a method for moving or translating warp yarn to form a shed. The apparatus includes a rigid, non-moving support frame which supports, in journalled fashion, spaced, parallel shafts. The shafts carry corresponding arcuate pulley members, between which run cables carrying lightweight heddle frames or carrying mail eye heddles, each pair forming a scroll. The scrolls are arranged in a nested manner on the non-moving frame. The scrolls can be selectively actuated to apply either an upward or downward force in tension to selectively translate the warp yarn to form the desired shed.
2. Description of the Prior Art
Various means have been previously utilized for shedding in weaving looms. Prior looms have included numerous, large moving support frames having upward and lower parallel shafts connected by end pieces, which support transverse heddle rods carrying vertical heddles therebetween. These moving frames have rigid or semirigid joints capable of transferring moment forces, and are commonly referred to as compact frames These rigid support frames are utilized to support the heddle rods, which maintain the eyes of each respective heddle both in a straight line and parallel to one another during shedding and at rest. Numerous support frames are grouped together with the warp yarn of the weaving loom passing through successive heddle eyes. Each support frame must be mechanically shifted either upwardly or downwardly in its entirety in order to create the shed. Many high speed looms currently used today, also employ rigid, moving support frames
In the past, when the typical weave rate was 60 to 100 picks per minute, the structural integrity of the support frames was not as critical as in present weaving loom frames. The prior support frames normally lasted for many years, and could be readily repaired by replacing one or more damaged components. Over the years, improvements in looms, especially in passing the weft yarn through the shed, have resulted in greatly increased weaving rates. Today, weaving looms of up to six feet in width which utilize movable support frames can achieve a cyclic weaving rate of 400 to 1,000 picks per minute, which is considered a high speed loom. This increase in weaving rate has dramatically increased the stress to which the support frames are subjected during the weaving action. This result in these higher stresses therefore, results in greatly increased fatigue and wear of the support frames and their associating biasing mechanisms.
During high speed weaving, the portion of the equipment providing the driving forces necessary to shift the support frames vertically up or down into the proper position must handle the vertical positioning of a large number of frames. High acceleration and deceleration forces are required to translate the support frames in a near vertical plane from the highest shed position to the lowest shed position. These movements must be accomplished during each pick. These forces create both deflection and stress in the frames and result in eyes which are unaligned.
To accomplish the weaving pattern desired, a dobby mechanism is frequently incorporated into the weaving machine to pull the support frames from their lowest position to their highest or upper position. The dobby works against forces of springs which provide the stored energy required to push the frames downward to their lowered position, when the dobby mechanism allows. The connecting link between the final crank of the dobby and the dobby lever is typically a cable which can exert force only in tension, and therefore is used to pull each frame into its uppermost position and also extend the tension springs, storing energy for the downward movement.
The high speed weaving machines of today use the support frames to support and position a large number of heddles, each heddle having an eye through which one end of the warp yarn passes. Many difficulties are also experienced in the service life of the heddles, which can fail due to fatigue, wear or other damage because of stresses transferred to the heddles by the current support frames. The modern heddles most used today are long, thin, flat stamped sheet metal elements which engage at either end the heddle rod supported by the shaft of the frame. The heddles are supported in a horizontal row, which may contain a thousand or more heddles A less frequently used alternative to the stamped, flat heddle is the mail eye wire or string heddle, which is also well suited for use with the invention described herein.
In an effort to compensate for the shorter life of and fatigue failures in the support frames, many changes have been made in their mechanical design in order to resist the effects of the increased stresses resulting from higher weaving rates. These changes have included utilizing stronger materials for the support frames, such as heat-treated aluminum alloy extrusions. Other advances now being tested have been to incorporate carbon fiber and other composite technology in the making of shafts. Even these newer support frame designs, however, are experiencing fatigue failures within unacceptably short service life. This fact, together with the higher cost of the modern-day support frames, necessitates that increasing weave rates above the rate achieved in today's weaving looms utilizing support frames, may be neither mechanically nor economically feasible. Therefore, while it may be possible to drive support frames at faster rates with corresponding advancements in inserting the weft yarn, it may be impractical to use high-technology support frames in high-speed weaving, because the support frames themselves had reached a fatigue limit barrier and are economically prohibitive.
In another prior art weaving loom, known as a Draper XP-2 Loom, a pair of rectangular support frames having shafts which support heddle rods and heddles are shifted in opposite directions, one up and the other down, to form a shed by a cam driven treadle system. One of the treadles is attached to the bottom of the first support frame, and the second treadle is attached to the bottom of the second frame with the top of the pair of frames connected to each other by flexible connection means over the top of a rotatable cylinder mounted at the ends in a horizontal position. A lever, or treadle, is attached at one end to each of the two frames, and driven near its other, pivoted end by a cam. The rotation of the cam drives one treadle downward and one frame down. This downward movement of one frame pulls the other frame upwardly, which is allowed upward movement by the other cam through the associated treadle. Major disadvantages of this device are: (1) that the gage or horizontal separation between the frames is controlled by the diameter of the cylinder; (2) it is adaptable to looms which utilize only two frames; and (3) the horizontal rotating cylinder is supported only at the ends. This type of machine is useful only in the simplest weaving operations, such as weaving non-patterned cloth.
In other prior art devices, various means are employed to shift rows of mail eye heddles without utilizing support frames. For example, U.S. Pat. No. 4,440,196 to Arvai, discloses an open-shed Jacquard machine having multiple modules of pulleys, to which are attached harness cords having mail eye heddles. The pulleys rotate in order to pull the harness cords against pre-tensioned springs to displace the mail eye upwardly. This device is primarily directed to the inclusion of individual harness cord displacing means to individually control each pulley independently of other pulleys, and to selectively control the height or lift at which each mail eye is displaced. This machine, however, is useful only for narrow, intricate weaving operations and has no general application to high-speed, wide-loom weaving. Another drawback of the device disclosed in U.S. Pat. No. 4,440,196 is that, as in other prior art weaving looms, the harness cord is biased upwardly against the tension exerted by a cord tensioning system or spring. This device, however, has the additional disadvantage of requiring a spring for each, respective mail eye.